ringdowns

A ringdown is a phenomenon observed in various physical systems, particularly in astrophysics and acoustics. It refers to the decaying oscillatory signal that a system emits after being disturbed. Imagine striking a bell; the initial loud sound is followed by a series of diminishing tones as the vibrations gradually cease. This fading sequence of sound is analogous to a ringdown.

In the context of black holes, the ringdown is the final stage of their inspiral and merger. When two black holes collide, they emit powerful gravitational waves. After the merger, the newly formed black hole is not perfectly spherical and undergoes a process of "quivering," emitting gravitational waves at specific frequencies that decay over time. Studying these ringdown waves allows scientists to confirm the properties of black holes predicted by Einstein's theory of general relativity.

Acoustic ringdowns are more common in everyday experience. Musical instruments like bells, gongs, and even stringed instruments produce ringdowns when struck or plucked. The specific frequencies and decay rates of these acoustic ringdowns depend on the material, shape, and size of the object. Understanding ringdowns is crucial for instrument design and sound engineering, as it dictates the sustained quality and character of the sound produced. The term can also be applied to electrical circuits or other resonant systems that exhibit similar decaying oscillatory behavior after an excitation.